Tach Issue

[Former_rotorhead]

When the car starts the tach moves to about 500 rpm. After revving it moves slightly to maybe 900, but won't go any higher. The motor will rev higher, but won't read on the tach. Anyone know of the location of the sending unit (I assume it is a sending unit)? Hopefully it's easy to get to.

[david hopwood]

matt

your tacho signal comes from the ecm pin 58 the fact the engine revs ok suggests the fault is probably in the guage itself as the tacho drive signal on this pin is derived from the crank pick up sensor used to switch the ignition coils.there are three connections on the tacho you should have 12v across two of them and a connection between the third terminal and emc 58 pin when running you should see a pulse on this pin varying in width with engine speed(you will need a oscilloscope for this )if you can confirm these are ok i would suspect you have dry joints in the electronics within the tacho

[Former_rotorhead]

Is the crank pick up sensor the same as the crank angle sensor? I've been having a fuel cut @ about 4900-5000 rpm's. It been like that since I first got her running. She did have a pretty bad electrical short before I owned the car. If the sensor was going bad or a connection is bad would that lead to the fuel cut, then the eventual demise of my tach?

[david hopwood]

fuel shutoff on v8 cars should be around 7000-7300 rpm the crank sensor used for firing commutation is mounted just to the side of the crankshaft pully it connects to the ecm pins 73-79 i know it is a long winded process but as you say you have had wiring problems in the past imho i think your only option would be to check out all relevent sensors connections to and from ecm ,voltages and integrity of ground connections

[Former_rotorhead]

Turns out I have a bad tach. Quote from repair shop is $600 for the part. D@MN!!!

[Günter]

the normal rev-counter, VDO-universal digital one ? .. is for example available 'used' here:

http://www.thelotusc...ize=50��(scroll down) to compare the size (diameter)

..and if you need the digital Speedo in 100mm diameter casing ..those are also still available, as far as it looks here ..but without Lotus badge on the dial of course

http://www.preissuch...Tachometer.html

Edited August 23, 2012 by Günter